It is remarkable to realise that as distinguished a medieval historian as the late Sir Michael Postan could quite recently characterise technical development as being 'remarkably static for the whole of the Middle Ages'. This static orthodoxy began to be questioned in the 1950s and 1960s, when A.C. Crombie and Lynn White Jr. pointed out that the impression of western man, since the scientific revolution, as essentially innovative and inventive, could also be gained from looking closely at the Middle Ages. As has so often been the case, since at least the twelfth century, what seems radical and challengingly unorthodox at one moment in time often becomes a new orthodoxy within two generations. It is now a commonplace that, at least in the later Middle Ages, scientific ideas and their technological applications changed and developed at least as rapidly as either philosophical ideas on the one hand or business techniques on the other.